1. Field of the Invention
The present invention relates to a method of forming a stamp face and a stamp face forming device for forming a stamp face using porous resin.
2. Description of Related Art
Conventionally, there are known stamps that use porous resin, such as polyurethane or polyethylene, which have continuous pores permitting ink to permeate. A stamp face comprising an ink permeable portion that permits ink to permeate and an ink impermeable portion that prohibits ink from permeating is formed by processing porous resin. According to a stamp having such a stamp face member, ink is previously impregnated in porous resin before stamping by press-contacting the stamp face onto recording paper wherein ink oozes out only from the ink permeable portion where a stamp pattern is formed to transfer an image onto recording paper.
FIG. 10 shows a conventional example of a stamp face forming device for forming the above-mentioned stamp face. According to a conventional stamp face forming device 405, a manuscript 402, a black sheet 404 and a stamp face member 401 formed from porous resin are laminated and held on a glass plane 450 acting as a support member and light is irradiated on the manuscript 402 by a light source 420. A stamp pattern is formed in the manuscript 402 by a portion thereof transmitting light and a portion thereof blocking light. A flash bulb or a stroboscope is used for the light source 420. A reflecting plate 425 is arranged around the light source 420, and light emitted from the light source 420 is reflected toward the manuscript 402.
Instead of using the black sheet 404, a black porous resin plate, which includes light absorbing fine particles, may be used as disclosed in Japanese Unexamined Patent Publication No. 50-31908. In this type of plate, the black porous resin plate itself absorbs light, and heat is generated therein.
Light that has transmitted through the portion of the manuscript 402 is absorbed by the black sheet 404, and heat is generated at the portion of the black sheet 404 receiving the light. The black sheet 404 and the stamp face member 401 are kept in close contact with each other. The portion of the stamp face member 401 in contact with the heat generating portion of the black sheet 401 becomes molten by the heat, thereby suppressing continuous porosity of the stamp face member 401 and forming a thin film layer that does not allow ink to permeate. Light incident on the portion of the manuscript 402 through which light does not transmit does not reach the black sheet 404, and, therefore, heat is not generated at the corresponding portion of the black sheet 404. The corresponding portion of the stamp face member 401 does not melt, thereby forming the ink permeable portion. In this way, the ink permeable portion and the ink impermeable portion are formed on the surface of the stamp face member 401 in accordance with the stamp pattern formed on the manuscript 402.
However, according to the above-mentioned conventional stamp face forming device, the manuscript 402, the black sheet 404 and the stamp face member 401 are mounted above the glass support plane 450. Therefore, when the stamp face is formed by using a manuscript having a comparatively large size, the distance between the light source and the manuscript or the black sheet significantly differs at the peripheral portion of the manuscript and at the central portion thereof. Thus, the amount of irradiated light significantly differs by the position on the manuscript face. That is, the amount of light is comparatively large in the vicinity of the central portion of the manuscript, and the amount of light is comparatively small at the peripheral portion of the manuscript. If the amount of irradiated light is excessively small, the continuous porosity of the stamp face member at the portion to be formed into the ink impermeable portion is not sufficiently suppressed thus permitting ink to permeate, which may form spotted stains during stamping. When the amount of irradiated light is excessively large, even adjacent portions of the stamp face member that are intended to serve as the ink permeable portion melt thereby causing thinned image lines for stamping.